This invention relates to a process for the preparation of virtually oligomer-free, monophasically storage stable cyanamide solutions in polyols. The invention also relates to monophasically storage stable mixtures containing 0.1 to 50 wt % of monomeric cyanamide in a polyol or polyol mixture.
It is known to use nitrogen-containing compounds such as urea, cyanamide, dicyanamide or melamine, as additives in polymers (e.g., polyurethane foams, particularly polyurethane flexible foams) to achieve improved flame resistance. See, for example, European Patent Application No. 4,618, German Offenlegungsschriften Nos. 2,348,838 and 2,043,917 and French Pat. No. 2,003,124.
One disadvantage of most nitrogen-containing flame retarding agents is the low solubility of these products in polyether polyols or polyester polyols. It is for this reason that they are normally used in the form of dispersions. Disadvantages of these dispersions include their low stability, their tendency to sedimentation and their high viscosity if their solids content is increased. These difficulties which create problems in continuous processes do not occur when pure, monomeric, solid cyanamide is used because monomeric cyanamide is readily soluble in polyols. However, pure, monomeric solid cyanamide is difficult to obtain technically and has low storage stability (di-/trimerization). Aqueous solutions of cyanamide are technically and economically obtainable but when aqueous cyanamide solutions are concentration by evaporation, oligomers which are difficultly soluble, relatively high molecular weight (e.g. dicyandiamide or higher homologues such as melamine) form. Monomeric cyanamide must therefore be extracted from this mixture with solvents such as ether. This extraction procedure is cost intensive.